ASMLib scans all disk devices during startup, or when using the oracleasm scandisk command, to search for disk header information to identify ASM disks. If there are multiple paths to one and the same disk, ASMLib will choose only one of the paths, because ASM cannot handle seeing the same disk twice. In a multipath environment, ASMLib needs to be configured to ignore individual device paths and instead use the multipath device name. If your previous multipath environment was configured properly it should have ORACLEASM_SCANORDER and/or ORACLEASM_SCANEXCLUDE defined. Here is a documentation link: